Standing seam roofs on pre-engineered metal buildings are formed of sheet metal (conventionally 24 gauge metal). The standing seam roof is supported by a sliding roof clip attached to purlins. Purlins are Z-shaped strips of metal (conventionally 14 gauge metal) supported by the building's outer walls and inner pavilions.
Many pre-engineered buildings are built with equipment installed on the roof, such as HVAC equipment, skylights, and the like (herein called roof equipment). Roof equipment is frequently installed while the pre-engineered building is being built, but may be subsequently installed on an existing roof by making an opening in the roof surrounded by a roof curb to support the equipment.
Roof curbs are used in the installation of roof equipment on a metal roof. Roof curbs are metal frames that are conventionally installed on stationary sub-framing supposed by the purlins to serve as supports for items of roof equipment. An item of roof equipment is conventionally mounted in sealed relation to the roof curb and the sheet metal roofing is installed on fixed stationary sub-framing that is attached to the purlins. Stationary sub-framing for roof curbs does not allow for thermal movement of the metal roofing panels.
Changes in temperature frequently cause sufficient thermal movement of the sheet metal roofing to loosen the weatherproof seals and result in undesirable leakage of water through the roof. The weatherproof seals are also loosened, resulting in leakage, when the roof is lifted from the purlins by sufficient negative pressure being created by the passage of wind across the roof.
One manufacturer of metal buildings uses the traditional method of fixed sub-framing but does not fasten the roof curb to the sub-framing. Instead, the 24 gauge roof panels are welded to the 14 gauge flange of the roof curb, with the expectation that the roof curb and the equipment it supports will move with the roof but thermal movement of the metal roof panels, caused by expansion and contraction of the metal roof panels due to changes in temperature, results in slotting or tearing of the lighter gauge roof panel and undesirable leaking.
To applicant's knowledge, there is nothing in the prior art that resists vertical uplift of a metal roof while enabling a roof curb to move as a metal roof moves in response to changes in thermal conditions.